Abstract

Background

In Italy, anthrax is endemic but occurs sporadically. During the summer of 2004, in
the Pollino National Park, Basilicata, Southern Italy, an anthrax epidemic consisting
of 41 outbreaks occurred; it claimed the lives of 124 animals belonging to different
mammal species. This study is a retrospective molecular epidemiological investigation
carried out on 53 isolates collected during the epidemic. A 25-loci Multiple Locus
VNTR Analysis (MLVA) MLVA was initially performed to define genetic relationships,
followed by an investigation of genetic diversity between epidemic strains through
Single Nucleotide Repeat (SNR) analysis.

Results

53 Bacillus anthracis strains were isolated. The 25-loci MLVA analysis identified all of them as belonging
to a single genotype, while the SNR analysis was able to detect the existence of five
subgenotypes (SGTs), allowing a detailed epidemic investigation. SGT-1 was the most
frequent (46/53); SGTs 2 (4/53), 3 (1/53) 4 (1/53) and 5 (1/53) were detected in the
remaining seven isolates.

Conclusions

The analysis revealed the prevalent spread, during this epidemic, of a single anthrax
clone. SGT-1 - widely distributed across the epidemic area and present throughout
the period in question - may, thus, be the ancestral form. SGTs 2, 3 and 4 differed
from SGT-1 at only one locus, suggesting that they could have evolved directly from
the latter during the course of this epidemic. SGT-5 differed from the other SGTs
at 2-3 loci. This isolate, thus, appears to be more distantly related to SGT-1 and
may not be a direct descendant of the lineage responsible for the majority of cases
in this epidemic. These data confirm the importance of molecular typing and subtyping
methods for in-depth epidemiological analyses of anthrax epidemics.